A technique that increases the amount of memory available in a virtual machine environment. Two popular approaches are memory ballooning and kernel same-page merging. Memory Ballooning This method allocates unused memory (RAM) from one virtual machine (VM) to another. The term symbolizes an "inflated" balloon temporarily residing in the memory of the VM it was taken from, making that memory unavailable. When the use of that memory is returned to the VM, the balloon is "deflated." Kernel Same-Page Merging (KSM) When active memory pages with duplicate content are found, they are merged into one and marked read-only. If an application modifies a merged page, a copy-on-write (CoW) page is created. See copy-on-write and virtual machine.